Laser power meters in the several watt to several hundred watt range include two general types: a mechanical probe similar to a meat thermometer provided with a heat sink at the tip and an electronic meter having a thermopile detector and remote read out unit.
The meat thermometer-type meter is "exposed" to the laser beam for a period of time, typically 20 seconds. The temperature rise is recorded by a mechanical needle movement from a bi-metal element in the probe. The temperature rise in the exposure period is proportional to input power. Except for the tip-mounted heat sink, the meat thermometer-type meter looks exactly like the commonly used meat thermometer and costs typically about $200.
The thermopile-based instrument records power continuously, with a delay time of less than 1 second. This is a large, precise laboratory instrument costing typically about $2,000. The thermopile-based instrument is used to tune and optimize lasers. It includes a "power head" that is separated from a display console by a cable.
Although the meat thermometer-type meter is fairly portable, it is both inaccurate and slow. The meat thermometer-type meter requires a separate stopwatch to measure the exposure period. As the exposure timing is critical for accurate power measurement, the meat thermometer-type meter has been found to be deficient. Further, the exposure time is relatively long and a long time is required between uses to let the heat sink cool. The required delay between uses is typically a few minutes.
The limitation on the thermopile instrument is not in the performance and accuracy area. Its limitation is portability. The power head is large as it is designed for continuous duty. In many cases, the power head cannot be inserted into an existing beam delivery system because of its large size. Further, the separation of the power head from the display console renders the thermopile instrument somewhat less than ideal in terms of ease of use.